Linked-list data structures store sequences of data elements, and provide the ability to rapidly add and remove data elements from such sequences. Linked-list data structures are characterized in that each element thereof includes a pointer to the next sequential element in the linked-list. Accordingly, it will be appreciated that the addition of an element to, or the removal of an element from, the linked-list data structure requires that the pointer of the immediately preceding element be updated to reflect the modification to the linked-list data structure.
Multi-threaded programs include a number of threads, a number of which may require access to a particular linked-list data structure. Such threads may perform either non-modifying operations, such as GETs, or modifying operations, such as ADDs, with respect to the linked-list data structure. In order to prevent simultaneous accesses by a number of threads to an object, such as a link-listed data structure, it is common practice for such threads to implement so-called "synchronized" methods, which perform a lock action on the target object, thus preventing any other methods from gaining access to the target object until that object is again unlocked by the active method.
Where the target object is a linked-list data structure, this entire data structure is thus typically locked by a synchronized method until that method completes. Accordingly, concurrent accesses by different threads to a linked-list data structure are prohibited.